Invasive species lose many co-evolved pathogens and parasites after translocation, but are also faced with novel selection pressures in an introduced range. Thus, the predicted immune profile of an invader involves investment in components of the immune system that are energetically inexpensive, rather than in those that produce excessive inflammation. Because some invaders remain near the site of introduction while others may disperse to novel environments, comparisons between range core and invasion front populations of an invasive species may provide similar results to those between native and newly invasive populations. Since their introduction to Queensland in 1935, cane toads have exhibited remarkable phenotypic flexibility, including in immune function, as their range has expanded across northern Australia. However, the genetic underpinnings of population-level differences in toad immune function have yet to be explored. We sought to investigate whether gene expression differences across toad populations matched predictions about invader immune profiles.
Spleen RNAseq data from toads across their Australian range was used to perform differential expression analysis.
Pro-inflammatory genes had higher expression at the ends of the range, while anti-inflammatory genes had higher expression in the middle. Middle populations down-regulated cytotoxic natural killer cells, and up-regulated genes involved in immunoglobulin diversification. These results were consistent with expression patterns across the range determined by soft clustering.
Our results suggest that there is indeed an invader immune profile, which may provide insight into how vertebrates cope immunologically with changing environments.
Australian Research Council [FL120100074, DE150101393]